Facebook has an office in Brazil. I don't really understand why they couldn't just levy financial penalties, since Facebook does actually have a business presence in the country.
WhatsApp and Facebook are still separate legal entities as far as i know, the subpoena was issued to WhatsApp it didn't comply they've issued a court order to block it in order to compel it to comply.
If a US company would not comply to a court order, a US judge can prevent the company from operating at all by freezing all of their assets and halting all of their operations.
You're presuming that that Facebook office in Brazil actually has a lot of assets in Brazil to seize. It's likely that it's a shell organisation and has nothing to seize.
